1. Field of the Invention
The present invention relates to a method of forming an isolation region involved in a semiconductor device, and more particularly to a method of fabricating a semiconductor device having an isolation region of trench type.
2. Description of the Related Art
As the integration of semiconductor devices increases, the separation area between the devices has been made smaller every generation. A conventional local oxidation of silicon (LOCOS) process for submicron technologies is limited by oxide encroachment, as well as by nonplanar surface topographies and the field-thinning effect. A device separation area of trench type has also been used.
The conventional method of forming a device isolation region of trench type will be explained with reference to FIGS. 1A, 1B and 2.
One of the conventional methods will now be described with FIGS. 1A and 1B.
First, as shown in FIG. 1A, a silicon oxide film 11 and a silicon nitride film 12 are formed, in order, on the semiconductor substrate 10. The silicon oxide film 11 and the silicon nitride film 12 are patterned so as to form an opening having a predetermined size. The etching process is accomplished by using the patterned silicon oxide film 11 and silicon nitride film 12 as a mask so that the semiconductor substrate 10 forming a trench groove, only directly under the opening region of the silicon oxide film 11 and the silicon nitride film 12, is removed. As a result of these steps, a trench groove having predetermined size is formed in the semiconductor substrate 10. The trench groove surface is etched to remove defects, and a silicon oxide film 13 is formed so as to cover the entire surface of the inner walls of the trench groove. The silicon oxide film 13 is provided as a protection film to remove the defect of surface and to obtain a fine deposition of the device separation film.
As shown in FIG. 1B, sequentially, an oxide film 14a and 14b are deposited on the silicon oxide film 13 covering the inner wall surface of the trench groove so that the trench groove is completely filled with the oxide film. The oxide film 14a and 14b are etched back on the entire surface so as to obtain a device isolation region of trench type.
However, a device separation film having a fixed thickness can be obtained in the narrow trench region by this method, but the surface of the semiconductor substrate in the wide trench region is exposed.
Another conventional method illustrated in FIG. 2 is adapted to solve the above mentioned problem that the surface of the semiconductor substrate is exposed due to entire surface etching. Another conventional method will be now described in conjunction with FIG. 2.
First, a silicon oxide film 21 and a silicon nitride film 22 are formed, in order, on the semiconductor substrate 20. The silicon oxide film 21 and the silicon nitride film 22 are patterned so as to form an opening having a predetermined size. The etching process is accomplished by using the patterned silicon oxide film 11 and the silicon nitride film 22 as a mask so that the semiconductor substrate 20 forming a trench groove is removed only directly under the opening region of the silicon oxide film 21 and the silicon nitride film 22. As a result of these steps, a trench groove having predetermined size is formed in the semiconductor substrate 20. The trench groove surface is etched to remove defects, and a silicon oxide film 23 is formed so as to cover the entire surface of the inner walls of the trench groove. The silicon oxide film 23 is provided as a protection oxide film so as to obtain a fine deposition of the device separation film.
Sequentially, an oxide film 24a and 24b are deposited on the silicon oxide film 23 covering the inner wall surface of the trench groove so that the trench groove is completely filled with the oxide film. Further, the oxide film 24a and 24b, except within the trench groove, are unnecessary for the device. Thus, an etch back process is carried out by chemical mechanical polishing (CMP) for the removal of the deposited oxide film, except within the trench groove. By such etch back process, the oxide film is removed so as to remain the oxide film 24a and 24b within the trench groove only. Therefore, a device isolation region of trench type can be obtained.
However, this method also has the problem of dishing in a relatively wide trench. The dishing may decrease the reliability of the semiconductor device due to the thickness decrease of the device isolation film.